Comparing Walden to Wobegon -- what kettle lakes mean to America

Friday afternoons in July mean a lot of Minnesotans are on their way to the lake. All Things Considered host Tom Crann sat down with a former Minnesotan who's written a detailed history of the lakes we find in our region.

Most of Minnesota 10,000-plus lakes are what geologists call kettle lakes. So are most of the lakes in New England, including the famous Walden Pond. But Minnesotans and New Englanders approach their lakes very differently.

Geology professor Robert Thorson's new book is called "Beyond Walden -- The hidden history of America's Kettle Lakes." Tom Crann met him at one of those lakes, Lake Calhoun in Minneapolis, to ask what defines it -- and so many others -- as kettles.